1. Field of the Invention
Embodiments of the present invention relate generally to optical communication systems and components and, more particularly, to an optical switching device with a reconfigurable channel spacing.
2. Description of the Related Art
In a wavelength division multiplexing (WDM) optical communication system, information is carried by multiple channels, each channel having a unique wavelength. WDM allows transmission of data from different sources over the same fiber optic link simultaneously, since each data source is assigned a dedicated channel. The result is an optical communication link with an aggregate bandwidth that increases with the number of wavelengths, or channels, incorporated into the WDM signal. In this way, WDM technology maximizes the use of an available fiber optic infrastructure; what would normally require multiple optic links or fibers instead requires only one.
As bandwidth requirements for optical communication networks increase, it is desirable to increase the amount of information carried by a single optical fiber. This is typically accomplished by increasing the number of channels in a WDM carried by a fiber, and therefore decreasing the channel spacing of the WDM signal. Channel spacing is the amount of bandwidth allotted to each channel in a WDM communications system, and is defined as the spacing between center wavelengths of adjacent optical channels. For example, a fiber may carry a WDM signal that consists of 10 wavelength channels with a channel spacing of 100 GHz. When the channel spacing of the WDM signal is reduced to 50 GHz, the same fiber may instead carry 20 channels. Therefore, increasing the number of channels in a WDM signal increases the information-carrying capacity of an optical communications network without replacing or increasing the number of fibers in the optical communications network.
However, to convert an existing optical communications network to process WDM signals having a narrower channel spacing, other network hardware must be replaced, including lasers, wavelength lockers, and optical switches, among others. A wavelength selective switch (WSS) is one such component. A WSS is an optical switching device that routes each wavelength channel of a WDM signal from a common input port to one or more output ports. Because a WSS is configured to process a fixed number of wavelength channels with a fixed channel spacing, when the number of wavelength channels of the WDM is increased, the WSS can no longer perform its intended routing function. Hence, for the network to process the more closely packed WDM signal, each WSS contained therein must be either replaced outright or augmented with additional components, such as interleavers and supplemental WSS's. In either case, significant expense and system down-time are associated with the deployment of new optical switching components to enable processing of a WDM with a new, narrower channel spacing. Other optical switching components that require augmentation or replacement include optical add-drop multiplexers (OADMs), dynamic gain equalizers (DGEs), and wavelength selective routers, among others.
Accordingly, there is a need for optical switching devices used in communications networks, such as a WSS's, OADMs, DGEs, and wavelength routers, one wavelength channel spacing when initially deployed and capable of processing one or more narrower channel spacings as required without additional hardware modifications.